The term "plasma protein" means any and all of more than 100 different proteins occurring in plasma. Principal plasma proteins are albumin, globulin, various blood coagulation factors, fibrinogen, fibronectin, plasminogen, prothrombin and so on. For the fractionation of plasma into these and other plasma protein fractions, such techniques as Cohn's cold ethanol fractionation, ammonium sulfate fractionation and polyethylene glycol fractionation are known.
Of these plasma proteins, albumin and globulin are particularly useful for medicinal purposes and it is, therefore, common practice to first isolate these proteins and, then, separate and recover the other proteins from the residual fraction. For example, the prior art methods described hereinbefore have been employed.
However, the yields of minor components by these techniques are invariably so low that the techniques ar inevitably inefficient in terms of the overall fractionation yield.
Under the above circumstances, the inventors of the present invention through intensive and diligent research have found that various plasma proteins can be efficiently isolated from a plasma-containing material, particularly plasma, by combining certain processes in a defined sequence. The present invention is an outcome of the above endeavor and finding.